chromium/third_party/blink/web_tests/http/tests/security/mixedContent/resources/fetch-insecure-css-resources.css

@font-face {
    font-family: ahem;
    src: url(http://example.test:8080/css/resources/cors-ahem.php);
}

html {
    font-family: ahem;
    background-image: url(http://example.test:8080/resources/square20.png);
}